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All file systems perform the same basic functions, based on their fundamental goals:
the intelligent organization of data and efficient control of and access to that data. As
a result, most of them resemble each other to some extent, even if they are also different
from each other in important ways. Even if two PC file systems differ greatly in terms of
their internal architecture and structures, they can be made to resemble each
other closely in their outward appearance. For example, Windows NT will support both FAT
and NTFS partitions, which are totally different in terms of their internal structures,
but have virtually the same interface for the user (and for software applications).

UNIX has been around for many decades, making it the oldest of all file systems used on
PC hardware. UNIX file systems are also probably the most different from the other file
systems used on PC, both internally and externally (referring to how the user
accesses the file system). While most Windows users are accustomed to the Explorer-type
interface for managing files and folders, UNIX files are usually managed with discrete
text commands--similar to how DOS works (in fact, many principles of the FAT file system
are based on UNIX.). There are graphical UNIX shells as well, of course, but many UNIX
users (myself included) never use them.

The more important differences, however, are internal. UNIX file systems are designed
not for easy use, but for robustness, security and flexibility. UNIX file systems offer
the following features, and have for many years:

Excellent expandability, and support for large storage devices.

Directory-level and file-level security and access controls, including the ability to
control which users or groups of users can read, write or execute a file.

Very good performance and efficient operation.

The ability to create "flexible" file systems containing many different
devices, to combine devices and present them as a single file system, or to remotely mount
other storage devices for local use.

Facilities for effectively dealing with many users and programs in a multitasking
environment, while requiring a minimum of administration.

Ways to create special constructs such as logically linked files.

Reliability and robustness features such as journaling and support for RAID.

If these features sound similar to those of NTFS, that's because UNIX and Windows
NT/2000 now compete for much of the same market, so NTFS was given most of the
capabilities that UNIX has. There are many other features as well, which differ from one
implementation to another--there is no single "UNIX file system", any more than
there is a single "UNIX operating system". Each UNIX variant (including the
popular Linux for the PC, which itself has many different flavors) has a slightly
different file system, though they are of course very similar to each other, and it is
usually possible for different UNIX implementations to read each other's files.

UNIX file systems were one of the first (if not the first) to use the hierarchical
directory structure, with a root directory and nested subdirectories. (Most of us are
familiar with this from using it with the FAT file system, which works the same way). One
of the key characteristics of UNIX file systems is that virtually everything is
defined as being a file--regular text files are of course files, but so are executable
programs, directories, and even hardware devices are mapped to file names. This provides
tremendous flexibility to programmers and users, even if there is a bit of a learning
curve at first.

Since few PC users run UNIX on their own machines, it's unlikely that you will ever
actually use a UNIX file system directly. However, you may find yourself using a UNIX file
system if you run a web site, for example, so understanding the basics of how UNIX works
is a good idea. For more information, you may wish to consult this page,
which provides a nice overview of the file system. This page
provides more detail and also describes common UNIX file-manipulation commands. There are
literally thousands of other sites and pages about UNIX on the Internet!